Originally Posted by kurtisberry

Service manual says P0120 is the dual position sensors in the throttle body. Not the pedal or tune or leaks.

Having researched the pedal sensors, to design a sprint booster clone, I found that it is also a dual system. Failure or the primary sensor causes a switch over to the secondary sensor. The secondary sensor only puts out about 40% of the voltage of the primary. So limp mode is 40% full throttle. I would guess the same thing applies to the throttle side, but reverse.